Combined rectifier and amplifier circuit



p 13, 1932- K. c. BLACK 1,876,841

COMBINED RECTIFIER AND AMPLIFIEII CIRCUIT Filed April 25. 1930 2 Sheets-Sheet 1 7?: .1. mong? g 1 L 1 a/ a +ba/ Z a v 7 7 I gwuento'o:

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S p 13, 1932- K. c. BLACK 1,876,841

COMBINED RECTIFIER AND AMPLIFIER CIRCUIT Filed April 25. 1930 2 Sheets-Sheet 2 Patented Sept. 13, 1932 UNITED "STATES PATENT" OFFICE:

KNOX CHARLTON BLACK, OF BOONTON, JERSEY, ASSIGNOR, BY MESNE ASSIGN- MEN TS, '10 RADIO CORPORATION 01 AMERICA, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE Application filed April 25,

This invention relates to vacuum tube circuits and more particularly to methods of and circuits for employing a multi-element vacuum tube both as a demodulator or rectifier of carrier wave signals and as an amplifier for the signal voltage and/or the rectified voltage.

In accordance with the invention, the external circuits of a multi-element vacuum 1 tube are so arranged that the cathode and another element function as a diode rectifier, and the cathode and two or more additional elements function as an amplifier.

v The amplification may precede or may follow the rectification, or reflex circuits may be provided for amplifying both before and after rectification. The known commercial tetrode and pentode tubes having coaxial, cylindrical elements may be employed, but for some circuit arrangements, improved operation may be attained when the element acting as the anode for diode rectification is positioned outside of the electron stream established between the amplifier elements.

Objects of the invention are to providemcthods of and circuits for effecting both amplification and rectification of a signal with a single multi-element vacuum tube. More particularly, objects are to provide methods of and circuits for employing a multi-element tube for the rectification of a signal and for the amplification of the signal at carrier and/or audio frequencies.

These and other objects of the invention will be apparent from the following specification, when taken with the accompanying drawings, in which,

Fig. 1 is a circuit diagram of one embodiment of the invention,

Figs. 2a to 20 are fragmentary circuit diagrams illustrating other embodiments of the invention,

Figs. 3a to 3e illustrate forms of coupling devices which could be substituted in the circuit of Fig. 1,

Figs. 4, 5 and 6 illustrate reflex circuits for amplifying both before and after diode demodulation of the signal.

Operation in accordance with the present invention is predicated upon the fact that comnman RECTIFIER am) AMPLIFIER cmourr R S E D 1930. Serial No. 447,303.

'vacuum tube may be'a pentode having three grids serially arranged in the electron field c etween the cathode C and plate P. The inner grid G acts as a controlgrid for the amplification of the signal voltage across an input circuit 1, the bias being provided through resistance 2 by a battery 3. The outer grid G is connected to the cathode, and the intermediate grid Gr serves as the anode of a radio frequency amplifier. The amplifier anode circuit includes a source of current 4 and the primary winding of a radio frequency transformer 5.

The amplified radio frequency in the secondary of the transformer 5 is fed through a blocking condenser 6 of low radio frequency impedance to the plate P of the tube. The plate isvalso connected through the radio frequency choke 7 to the terminal 8 of the audio frequency output circuit. The other terminal 9 of the output circuit is connected to the cathode and a radio frequency by-pass condenser 10 and audio frequency resistance 11 are shunted across the output terminals 8, 9.

In this circuit, the plate P acts as the anode of an ordinary diode rectifier with parallel feed, i. e., the applied radio frequency voltage swings the plate positive during a part of the cycle and thereby causes rectified current to flow through the resistance 11 from the cathode to the plate. The circuit therefore acts as a combined radio frequency amplifier and diode detector and, so long as distortionless carrier amplification is afforded by the inner elements, the audio output will be a linear function of the applied radio frequency carrier amplitude and degree of modulation within those limits for which the customary diode causes this linear relation.

The circuit connections for securing both 100 amplification and diode rectification may be varied within wide limits. For convenlence of description, the respective upper terminals of the transformer windings in F ig. 1 are designated as a, b, and the low potential or grounded terminals of the primary and secondary windings are designated as a, d, re-

spectively. The incomplete diagrams, Figs.

2a, 2b and 20, show alternative connections to the vacuum tube. In these views, the terminals a, b, indicate the points of the network which are to be connected to that part of the stage network of Fig. 1 which lies to the right of points a, b of that figure. As shown in Fig. 2a, the carrier voltage may be impressed upon the inner grid G the grid G'r constitutes a screen grid and the outer id G is the anode element of the radio equency amplifier. In the circuit of Fig. 2b, the grid G is a space charge grid, the signail is impressed u on the intermediate grid G, and the grid 3 is the amplifier anode. The Fig. 2c circuit shows the connections for a tetrode tube in which the inner grid (it constitutes the control grid and the outer grid G is the amplifier anode.

The series of views, Figs. 3a to 3e, show various forms of inductive coupling that may be employed between the amplifier anode circuit and the rectifier circuit. Any one of these coupling devices may be substituted for the transformer shown in Fig. 1 by connecting the terminals a, 6, etc., to be correspondingly identified points of the Fig. 1 circuit. Fig. 3a shows a transformer coupling in which the direction of the windings is re versed; Fig. 3b shows an inductive impedance coupling Fig. 3c shows an audio transformer coupling; and Figs. 3d and 36 show transformer couplings including a variable condenser C for adjusting the coupling circuit to resonance. Resistive or capacitive couplings may be employed and their design will be obvious to any person familiar with the construction and operation of radio frequency circuits.

When the performance of an amplifier-detector circuit is investigated, it will be found that the output voltage is a substantially linear function of the carrier voltage for signals falling within the range of values for which the amplifier elements act as a distortionless amplifier. \Vith certain circuit conditions the emission of secondary electrons from the plate or diode element of the tube will give a non-linear response but, in general, the limitation of the linear region is due;i to overloading of the radio frequency ampli er.

The amplifier detector circuit contemplated b the invention presents the possibility o reflexing or feeding the audio voltage back onto the original control grid for further amplification of the signal at audio frequency. The reflex-circuit shown in Fig. 4 employs the general circuit arrangement which is shown in Fig. 1 and corresponding elements of these two views are identified by the same reference numerals.

The transfer of amplified radio frequency voltage from the amplifier anode circuit to the rectifier circuit is effected by a radio frequency choke 5 that will be recognized as the coupling element shown in F i. 3?). The secondary winding 12 of an audio frequency transformer is connected between the cathode C and the tuned input circuit 1, the winding 12 being shunted by a radio frequency bypass condenser 13. The primary 14 of the audio frequency transformer is connected through a condenser 15 of low audio frequency impedance to a tap 16 that may be adjusted along the resistance 11, and to the tube cathode. The amplified audio frequency output is made available across the terminals 8, 9' of a transformer whose primary Winding 17 is connected between the radio frequency choke 5' and the cathode. The operation of this reflex circuit will be apparent from the above description of the Fig. 1 circuit.

The reflex circuits of Figs. 5 and 6 show possible arrangements in which two tubes operate in parallel for radio frequency amplification and diode rectification, and in push-pull for audio frequencies. The general system of circuit connections is shown in Fig. 2a, i. e., the amplifier action is essentially that of a triode having a screen grid.

In the arrangement shown in Fig. 5, the radio frequency input circuits for the tubes 18, 19 are substantially identical inductances 20 which may be simultaneously tuned to resonance by the variable condenser 21 and which may be, due to the blocking condensers 22, at different direct current or radio frequency potentials. The high potential terminals of the inductances 20 are connected to the control grids G of the respective tubes, and the low potential terminals are connected to the cathode through the radio frequency by-pass condensers 23.

The iductances 20 are conductively connected to the cathodes through the secondary windings 24 of an audio frequency transformer and the bias battery 25. The outer grids G3 constitute the amplifier anode elements and arevconnected to the cathodes through radio frequency chokes 26 and the primary windings 27 of an audio frequency push-pull transformer, the windings being shunted by radio frequency by-pass condensers 28. The respective amplifier anodes are connected to the plates P through the radio frequency condensers 29, the plates P being connected through the common radio frequency choke 30 to the audio frequency resistance 31 which is by-passed for radio frequencies by the condenser 32. The desired portion of the audio frequency voltage developed in the resistance 31 by the diode rectifier action is impressed, through the tap 33 and audio frequency condenser 34, upon the primary winding 35 of the push-pull-transformer whose secondary windin s 24 are included in the input circuits of t e respective tubes. The Fig. 6 arrangement is a simplified modification of the Fig. 5 circuit which may not be desirable for all purposes since there is some degeneration due to the fact that the audio frequency impedances in the respective input circuits are also elements in the amplifier anode circuits of the respective tubes. The tuned input circuit 1 impresses the radio frequency signal in parallel upon the control grids G of tubes 18, 19. The general arrangement of the amplifier output circuits and the diode rectifier circuits may be substantially identical with that shown in Fig. 5, and corresponding elements of the two views will not be described in detail but are identified by the same reference numerals.

Attention is directed to the fact that, in the Fig. 6 circuit, only the tube 18 acts as a rectifier for the amplified radio frequency output of both tube 18 and tube 19. Tubes 18 and 19 are both shown as pentodes, no connection being made to the plate P of tube 19, but it is obvious that tube 19 may be apentode. Tube 18 is preferably of the type described in my copending application, Ser. No. 446,098, filed April 21, 1930.

The secondar windings 24 of the audio frequency trans ormer are serially connected between the cathodes of tubes 18, 19, and the low potential terminal of the tuned input circuit 1. As stated above, this arrangement of the windings 24 as elements common to the grid and anode circuits of the amplifier will result in some degeneration, but this sim-' plified circuit arrangement may be employed where high amplification is not essential.

Since these reflex circuits demonstrate the possibility of diode rectification and audio frequency amplification with a single tube, it will be apparent that the impressed radio frequency signal could be applied directly to the diode rectifier circuit. This use of a multi-element tube as a diode rectifier and audio frequency amplifier is described and claimed in my copending application Serial Number 446,755, filed April 23, 1930.

The method of operation by which radio frequency amplification is followed by diode detection has the special advantage that the operation of the preceding radio frequency amplifier stage is not affected by the diode rectification. The customary method of feeding a diode rectifier directly from the preceding amplifier stage is open to the objection that the diode, being a power consuming device, loads the input circuit of the amplifier stage and reduces the gain and selectivity. When the diode rectifier is fed,

in accordance with this invention, from an additional amplifier stage comprising ele ments of the same vacuum tube, greater inherent sensitivit is 'obtained, due to the amplification in t e amplifier-detector stage, and the gain and selectivity of the preceding stage are maintained at their normal values.

It will be understood that the specific circuits which are shown in the drawings are merely illustrative of the invention and that there is a wide latitude in the choice of tube constructions and of circuit arrangements for effecting operation in accordance with the spirit of my invention as set forth in the following claims.

I claim:

1. In a combined amplifier-detector stage, the combination with a vacuum tube having a cathode and a plurality of elements, of circuit connections between one of said elements and said cathode to constitute a diode rectifier, and circuit connections cooperating with a plurality of other elements and said cathode to constitute amplifier input and output circuits.

2. The combination with a vacuum tube having a cathode, a diode element, a control grid and an implifier anode, of impedances associated with said cathode and diode element to constitute a diode rectifier circuit; impedances associated with said cathode, grid and anode to constitute amplifier input and output circuits, and coupling between certain of said impedances to transfer signal energy between said rectifier circuit and one of said amplifier circuits, whereby the signal may be amplified and rectified by said vacuum tu e.

3. The combination with a vacuum tube having a cathode, a diode element, a control grid and an amplifier anode; input and output circuits associated with said grid and anode, and means for impressing a carrier wave signal upon said input circuit; of a rectifier circuit connected between said cathode and said diode element, and means coupling said output circuit to said rectifier circuit.

4. The invention as set forth in the above claim 3, in combination with means for impressing upon said input circuit the audio frequency voltage developed in said rectifier circuit, and an audio frequency impedance in the said output circuit.

5. In combination, an electron discharge tube provided with an anode, cathode, and at least two auxiliary electrodes, a diode rectifier circuit connected between the cathode and said anode, an amplifier input circuit between said cathode and one of said electrodes, and an amplifier output circuit connected between said cathode and the remaining auxiliary electrode.

6. In combination, an electron discharge tube provided with an anode, cathode, and at least two auxiliary electrodes, a diode rectifier circuit connected between the cathode and'said anode, an amplifier input circuit between said cathode and one of said electrodes, and an amplifier output circuit connected between said cathode and the remaining auxiliary electrode, and additional means for coupling said output circuit to said rectifier circuit.

7. In combination, an electron discharge tube provided with an anode, cathode, and at least two auxiliary electrodes, a diode rectifier circuit connected between thecathode and said anode, an amplifier input circuit between said cathode and one of said. eleo-= trodes, and an amplifier output circuit connected between said cathode and the remaining auxiliary electrode, said auxiliary electrodes being maintained at diiierent potentials.

8. A receiver comprising" a tube provided with a cathode, a diode element, a control grid and an amplifier grid, a source of signal energy coupled to said control grid and cathode, a rectifier circuit between said cathode and diode element, on amplifier circuit coupled to said cathode, amplifier grid and diode element and a load circuit cou led to said rectifier circuit.

9. A receiver comprising a tube provided with a cathode, a diode element, a control grid and an amplifier grid, source of signal energy coupled to said control grid and cathode, a rectifier circuit between said cathode and diode element, amplifier circuit coupled tosaid cathode, amplifier grid and diode element, and a load circuit coupled to said rectifier circuit, and additional means for coupling the load circuit to said control grid and cathode.

10. An electrical circuit comprising" a space discharge tube provided with a cathode, a positive cold electrode, and at least two additional cold electrodes, a liode rectifier circuit connected between the said cathode and said positive electrode, a high frequency source coupled bet-ween the cathode and one of said additional electrodes, and an output circuit coupled between the cathode and the remaining one of said additional cold electrodes.

11. An electrical circuit comprising a space discharge tube provided with a cathode, a positive cold electrode, and at least two ad ditional cold electrodes, a diode rectifier circuit connected between the said cathode and said positive electrode, a high frequency source coupled between the cathode and one of said additional electrodes, and an output circuit coupled between the cathode and the remaining one of said additional cold electrodes, and an auxiliary cold electrode within said tube at cathode potential.

12. The combination with a vacuum tube having a cathode, a. diode element, a control one of said electrodes,

grid and'an amplifier anode, of impedance associated with said cathode and diode e ement to constitute a diode rectifier circu t;

im ed'ances associated with said cathode, d an anode to constitute amplifier mput a d output circuits, and couplin between certain of said impedances to trans er signal energy between said rectifier circuit and one of said amplifier circuits, whereby the signal may be amplified and rectified by said vacuum tube, a second tube provided with a cathode, element, control grid and amplifier anode, and electrode circuits corresponding to those of the first tube connected to the electrodes of the second tube.

13. The combination with a having a cathode, a diode element, a L grid and an amplifier enode,of impedanes associated with said cathode and diode ment to constitute diode rectifier cir impedances associated with said cathode, grid and anode to constitute amplifier output circuits, and condensive coupling between certain of said. impedances to transfer signal energy between said rectifier circuit and one of said amplifier circuit, whereby the signal may be amplified and rectified by said vacuum tube.

14-. lln combination, electron discharge least two auxiliary electrodes, diode rectifier circuit connected between the cathode and said anode,an amplifier input circuit hetween said cathode and one of said and an amplifier output circuit connected between said cathode and the remaining iliary electrode and means for connecting'said rectifier circuit with said input circuit.

15. in combination, an electron discharge tube provided with an anode, cathode, and a least two auxiliary electrodes, a diode rectifier circuit including a resistor connects between the cathode and'said anode, an amplitier input circuit between said cathode circuit connected between said cathode and the remaining auxiliary electrode and a connection between the resistor and the circuit. 7

16. In a combined amplifier-detector stage, the combination with a vacuum tube having a cathode and a plurality of elements, of circuit connections between one of said elements and said cathode to constitute a diode rectifier, circuit connections cooperating with a plurality of other elements and said cathode to constitute amplifier input and output circuits and a second tube having electrodes similar to said first tube, and electrode circuits corresponding to those of the first tube connected to the electrodes of the second tube.

in testimony whereof, Iaifix my signature.

KNOX CLTON BLACK.

and an amplifier output 

